1. Field of the Invention
The present invention relates to a safety valve of an accumulator in a fuel injection apparatus of a diesel engine for injecting high-pressure fuel accumulated in the accumulator by means of an injector of an electronic control type provided in each cylinder.
2. Description of the Prior Art
There has been conventionally known a fuel injection apparatus, as disclosed in Japanese Patent Unexamined Publication No. 59-165858, which is arranged in such a manner that high-pressure fuel is accumulated in an accumulator called a common rail by a high pressure supply pump, and the high-pressure fuel of the accumulator is injected by an injector of an electronic control type provided in each cylinder.
This fuel injection apparatus is provided with a safety valve which is opened for releasing the fuel when a pressure in the accumulator exceeds a predetermined value.
As shown in FIG. 5, the structure of the conventional safety valve is such that a tapered seat face 32 which is an opening portion of a passage 31 in communication with the accumulator is opened/closed by a ball valve 37, and that when the fuel pressure in the accumulator exceeds a biasing force of a spring 38 which presses and biases the ball valve 37 in a valve-closing direction, the ball valve 37 is opened to release the fuel of the accumulator to the low pressure side, thereby suppressing an increase of pressure in the accumulator.
With this structure, however, an area of an opening after the ball valve 37 is opened is insufficient. Consequently, even after the fuel has been once released through the opened valve, there is a risk that the pressure in the accumulator is increased to exceed a valve-opening pressure of the ball valve 37 when the fuel is pressurized and delivered again. Particularly when the fuel of a maximum flow rate Q.sub.max is pressurized and delivered from the high-pressure supply pump to the accumulator, there is a risk, as shown in FIG. 6, that the fuel pressure is increased to exceed not only the valve-opening pressure P.sub.0 but also a critical internal pressure P.sub.E of an accumulation piping.